This application is in response to RFA-MH-11-081: Reinvigorating HIV Prevention for Men who have Sex with Men (R21). Meth-using MSM (MUMSM), many of whom are polysubstance users, have double to triple the probability of engaging in unprotected anal intercourse, even with episodic use. When working with men not receptive to traditional condom-based prevention messages, a harm reduction approach has the potential to reinvigorate HIV prevention. If we can provide high-risk men with an intervention that meets their specific needs, we have a much greater chance of seeing measurable reductions in risky behavior. The long-term objective of this research is to develop a mobile online tool for MUMSM and educators serving this population that will facilitate a reduction in HIV transmission by supporting the enactment of harm reduction strategies, including increased condom use. Grounded in the Information- Motivation-Behavioral Skills (IMB) Model, the four aims of this R21 allow for the collection and analysis of formative data needed to develop the online tool. Aim 1 compares patterns of polysubstance use and harm reduction in MUMSM who meet male sexual partners online to identify differences in IMB and predictors of risk behavior. Aim 2 identifies how MUMSM in different harm reduction classifications vary in their perception of online HIV prevention needs, including preferred content and design features. Aim 3 identifies perceived online HIV- prevention needs, including preferred content and design features, of HIV-prevention educators who regularly conduct outreach and education for MUMSM. Aim 4 integrates quantitative and qualitative data to identify the IMB content and design features of an online HIV intervention for MUMSM. In addition to reaching high-risk MSM who might ignore current prevention messages, this application is significant because a mobile online intervention brings prevention to the risk environment where MUMSM are meeting men for substance use and sexual encounters. This tool also provides educators and case managers a mechanism to stay in contact with hard-to- reach MSM. This application is innovate because it proposes an efficient method to collect, analyze, and synthesize quantitative and qualitative data, and because it extends both the IMB and harm reduction models to a structural intervention by developing a mobile online tool that includes peer support for both MUMSM and prevention educators/case managers. A strength of this application is that it combines the expertise of the University of Minnesota HV/STI Intervention and Prevention Studies, a leader in Internet-based HIV prevention, with the expertise of a well- known researcher in prevention for MUMSM from the San Francisco Department of Health. PUBLIC HEALTH RELEVANCE: Internet-based HIV Prevention for Methamphetamine-Using MSM: Formative Research When working with methamphetamine-using men who have sex with men, a harm reduction approach has the potential to reinvigorate HIV prevention. An innovative intervention is needed for this high-risk population that both exhibits high-risk behaviors of polysubstance use and unprotected anal intercourse and rejects traditional condom-based prevention strategies. This study collects formative data needed to develop a mobile online tool that can offer tailored information, motivation, and behavioral skills content to methamphetamine using MSM, provide a means by which educators and case managers working with this population can stay in touch with their clients, and provide an e-infrastructure in which both methamphetamine-using MSM and educators and case managers can receive and provide social support for their harm reduction efforts.